The present invention relates to friction clutches, and more particularly to friction clutches in which engagement occurs at a predetermined speed in response to centrifugal force.
Friction clutches that engage at a predetermined speed have been known for some time and are particularly useful in combination with motors, such as internal combustion engines, that are not capable of starting under load conditions. The engine is permitted to accelerate freely with the clutch disengaged until it reaches the point on its power curve where it produces sufficient torque. At this predetermined speed, the clutch automatically engages and applies the load.
Previously known centrifugal friction clutches have exhibited a number of important shortcomings. Many are large and heavy, thus limiting the types of equipment on which they can be used. Some engage too abruptly or unevenly, causing the engine speed to fall. The engagement speed is usually not readily adjustable, and if adjustment is possible, disassembly of the mechanism and substitution of parts is often required. Another disadvantage of many previously known clutches is a tendency of the friction surfaces to remain engaged once engagement is commenced, resulting in a speed of disengagement substantially lower than the speed of engagement. If stalling on deceleration is to be avoided, the speed of engagement must be higher than otherwise desired to compensate for this effect.
An application of centrifugal friction clutches that is particularly demanding is the connection of a small displacement internal combustion engine to the drive wheel of a go-cart. These vehicles are not equipped with transmissions, and it is necessary to continuously engage and disengage the clutch as the cart enters straight-aways and turns. The clutch must be compact and light-weight, it must engage smoothly and always at the same speed, and the speeds of engagement and disengagement should be as close to each other as possible. Ease of adjustment of the speed of engagement is particularly important since the characteristics of different tracks dictate different optimum settings, and the best setting for an individual cart and driver must be determined by trial and error. The clutches presently used for this purpose must be disassembled for each readjustment, and their range of adjustment is relatively small.